The present invention relates to an Asynchronous Transfer Mode (ATM) network, a node device such as an ATM exchange applied thereto, and an alarm notification control method. More particularly present invention relates to an ATM network, a node device and an alarm notification cell transfer control method having a control function to perform selective transmission and restriction of an alarm notification signal for every Virtual Connection (VC) multiplexed on a fault Virtual Path (VP).
In the recommendation I.610 "B-ISDN operation and maintenance principles and functions" of ITU-T (International Telecommunication Union Telecommunication Standardization Sector) approved in WTSC (World Telecommunication Standardization Conference) in March 1993, an alarm notification method for "Permanent Virtual Connection (PVC)" that is, processing method of an alarm notification OAM (Operation and Maintenance cell), is prescribed. In PVC, holding time of a connection set up from an operation system is relatively long (normally, at least several hours or more).
In the ITU-T I.610, however, there is no prescription about an alarm notification method for "Switched Virtual Connection (SVC)" in which holding time of a connection set up by a call control processor of an exchange every time a call is generated is relatively short.
According to the recommendations of ITU-T I.610, when a fault of a Virtual Path (VP) is detected during the period of connection set-up, the processing of fault detection notification will be performed upon PVCs formed on a fault VP (hereinafter VCs: describing the processing on Virtual Channels by way of example) in the following procedures.
FIG. 4 shows a portion of an ATM network where an originating VC user terminal 401 and a terminating VC user terminal 405 are connected with each other through an originating node 402, a transit node 403 and a terminating node 404. Then, assume that a fault arises at a place designated by the x-mark 421 on a Virtual Path (VP) having an upstream Virtual Channel (VC) 419 where a signal (ATM cell) is transferred from the originating VC user terminal 401 to the terminating VC user terminal 405.
The above VP fault (a fault of a lower layer than the VP, or a fault of the VP itself) is detected by the transit node 403 adjacent to the downstream side of the fault place. The transit node 403 transmits a VC-AIS (VC-Alarm Indication Signal) cell 422 for alarm notification toward the downstream of the VC 419 multiplexed on the fault VP. The VC-AIS cell 422 is terminated at the terminating VC user terminal (first device) which is to be an end point of the upstream VC 419.
Recognizing a fault on the VC through reception of the above VC-AIS cell, the first device transmits a VC-RDI (VC-Remote Defect Indication) cell 423 to a downstream VC 420 paired with the fault VC (upstream VC 419). Although the cell 423 is described as "VC-FERF: VC-Far End Receive Failure" in the above-mentioned ITU-T I.610, it has been agreed that the title "FERF" is altered to the title "RDI".
This VC-RDI cell 423 is terminated at the originating VC user terminal (second device) which is to be an end point of the downstream VC 420. The second device detects the VC-RDI cell 423 so as to recognize that there is a fault place on the way of the upstream VC 419 which is a transmission side to this device.
In the current circumstance in which there are no recommendations in ITU-T I.610, however, this fault detection notification method in the aforementioned PVC is applied as it is to SVC having shorter holding time of a connection. In this case, VC user terminals are compelled to have a function to deal with a fault management OAM cell (VC-AIS/RDI cell) even in SVC communication in which holding time of a connection is so short that the probability of a fault is small.
If VC user terminals performing communication by SVC are allowed to have no function for dealing with a fault management OAM cell in order to eliminate useless functions and simplify the structure of the terminals, VC user terminals having function for dealing with a fault management OAM cell and these VC user terminals having no function therefor are allowed to exist in the same network and, accordingly, each of the node devices constituting the ATM network is required to have the faculty to deal with both VCs having necessity to transfer VC-AIS/RDI cells and VCs having no necessity to transfer VC-AIS/RDI cells when a fault is detected. In such a situation, the following problems arise:
(1) how the necessity or unnecessity to transfer VC-AIS/RDI is notified from a VC user terminal to a node device; PA1 (2) how the necessity or unnecessity to transfer VC-AIS/RDI in every VC is notified between node devices; and PA1 (3) how the necessity or unnecessity to transfer VC-AIS/RDI in every VC is judged in each of the node devices.